One of the major challenges operators face in deployment of 3G networks, such as UMTS, is the ability to provide broadband speeds to users throughout the entire cell. In typical network deployments, the users at the cell edge often get served with much smaller data rates compared to users closer to the base station. While proper link budget planning and cell site placement can ensure that users at the cell edge are able to achieve a minimum desired data rate (e.g., 64 kbps average throughput), the reality is that cell site locations from existing 2G deployments will be used, making such minimum desired data rates difficult to achieve.
Exacerbating the situation even further, the 2G network (e.g., GSM) may be operating in the 850 MHz band, whereas the 3G network is operating in both the 850 MHz band as well as the 1900 MHz band. The significantly increased path loss experienced at the higher carrier frequency limits the data rates that users can see at the cell edge even further; this is especially a problem in the uplink as the mobiles typically transmit at relatively lower power levels (e.g., 125 mW). As such, it may be more difficult to achieve both higher capacity and higher cell edge rates in 3G deployment.
Cell throughput may be traded off against improved user data rates at the edge of the cell. Unfortunately, the current mechanism for switching carriers (sometimes referred to as carrier handoff or inter-frequency handoff) is a lengthy process, taking up to 5 seconds to carry out. This type of delay is not acceptable in mobile wireless environments with potentially higher vehicle speeds and may prohibit the use of user location information to improve system performance.